When stopping ugidfw, it is not enough to just try unloading the module. If
the module is built-in to the kernel then the kldunload will fail. Rather
than do this just check if there are rules and then remove them all.

Add requirement on FILESYSTEMS to ensure /usr is present for /usr/sbin/ugidfw
and /usr/bin/xargs. This was already effectively the ordering from rcorder(8).

MFC after: 2 weeks
Relnotes: yes